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Abstract

Gangliosides are complex glycosphingolipids derived from glucosylceramide or galactosylceramide and contain sialic acid in their carbohydrate chain. Sialidases, known also as neurominidases, are a family of glycohydrolytic enzymes functioning in the catabolism of sialoglycoconjugates by removing α-glycosidically linked sialic acid residues. Sialidase Neu4 is the lysosomal sialidase and GM2 activator protein is the cofactor of β-Hexosaminidase a enzyme to degrade the GM2 ganglioside. The activity of sialidase Neu4 activity against GD1a and GM2 gangliosides were significantly increased by the co-transfection with GM2 activator protein to the cells transfected with sialidase Neu4. This in vitro study revealed that lipid-binding proteins can facilitate the glycolipid degradation rendered by sialidase Neu4 in the lysosomes. In the concept of this study, a systematic comparison of the storage levels of gangliosides, gene expression ratios and behavioral features of new double (Hexa-/-GM2AP-/- and GM2AP-/-Neu4-/-) and triple (Hexa-/-GM2AP-/-Neu4-/-) knockout mice models with the existing double (Neu4-/-Hexa-/-) and single (Hexa-/-) knockout models revealed the possible involvement of the GM2 activator protein as a cofactor of sialidase Neu4 in the bypass mechanism in the Tay-Sachs mice, in vivo. Based on the increased GM2 ganglioside level in brain and cerebellum detected by the immunohistochemical and imaging mass spectrometric analysis, we speculate that the sialidase Neu4 functions on the degradation of GM2 ganglioside with GM2 activator protein, in vivo.